Thanks for your thoughtful response.

It should be noted that it would make the site exclusive to people who don't tick everyone else off.

True, but if you set the threshold high enough, it would take a lot to meet it. Say if someone's overall rep for a week is below -100, or if his ratio of downvotes to upvotes is below some level, there's a call for a vote on whether to boot him, for instance. Dunno what the exact number would need to be, but I'd think something like that would be possible without people having to fear that annoying the wrong person or having a bad day would get them banned.

Of course, that would require coding too, and discussion when a vote came up, so that's not a free solution either. But it seems to me like a reasonable extension of the reputation concept, if people wanted to do it.